The present invention relates to radiation image processing apparatus and cassettes for storing a radiation image, and specifically relates to a radiation image processing apparatus and a cassette for storing a radiation image, in which a stepwise variation of density formed on a wedge area of a radiation image is utilized for adjusting a gradation and a suspicious region detecting parameter of the radiation image.
Conventionally, before an image is printed out onto a film or a paper, or displayed on the high-luminance CRT monitor, etc., various kinds of image adjustments, such as manual adjustment of gradation, gradation processing, frequency processing, dynamic-range compression processing, multi-objective frequency processing, etc., are applied to the image data of the image to be outputted.
Mammography has been known as one of reliable methods to detect breast cancer, and recently, frequently introduced into mass examinations. The densities of mammary glands in mammograms widely vary depending on individualities and ages of subjects, and generally, mammary glands of a young lady or a nullipara are very high dense and uniform. However, involution of mammary glands and fatty degeneration advances with the increase of age, resulting in uneven density of mammary glands, which will be finally substituted by adipose tissues. To distinguish the mammary glands from other tissues, the radiation images have been classified into several types.
Further, in case of conventional processes for detecting a suspicious region, the suspicious region detecting means in the film-screen system utilizes image data obtained by digitizing the film image, while that in the digital system utilizes image data inputted from the inputting device as it is.
In order to alleviate the doctor's labor for reading the radiation image and to reduce oversight cases on the doctor's part when the doctor makes diagnosis while viewing a radiation image, processes for detecting a candidate region as a suspicious region by means of a computer have been developed. The methods for detecting a mass shadow and a microcalcification, which are known as major two findings in case of the breast cancer, have been widely proposed.
(References with Respect to the Major Two Findings in Case of the Breast Cancer)
1) Mass Shadow
Computerized detection of masses in digital mammography: Automated alignment of breast images and its effect on bilateral-subtraction technique (Med. Phys., Vol. 21. No. 3, 445-452)
Detecting method by employing iris filter (Trans. Inst. Electron. Inform. Commun. Eng. D-11, Vol. J75-D-11, no. 3, pp. 663-670, 1992)
Detecting method by employing Quoit filter (Trans. Inst. Electron. Inform. Commun. Eng. D-11, Vol. J76-D-11, no. 3, pp. 279-287, 1993)
Detecting method by conducting binary-coding operation on the basis of histogram of pixel values of segmented breast regions (Jamit Frontier 95, collection of lectures, pp. 84-85, 1995)
Minimum directive difference components filter for acquiring minimum output from many Laplacian filters having directivity (Trans. Inst. Electron. Inform. Commun. Eng. D-11, Vol. J76-D-11, no. 2, pp. 241-249, 1993)
2) Cluster of Microcalcifications
Method for eliminating quasi-positive candidate regions, on the basis of optical density deference of shadow images, standard deviation values of boundary density deference, etc., by regionalizing a region suspected to be microcalcifications from a breast area (IEEE Trans. Biomed Eng BME-26 (4): 213-219, 1979)
Detecting method by employing images to which Laplacian filtering processing is applied (Trans. Inst. Electron. Inform. Commun. Eng. D-11, Vol. J71-D-11, no. 10, pp. 1994-2001, 1998)
Detecting method by employing images to which morphorgy analysis is applied to suppress influence of background patterns including mammary glands, etc. (Trans. Inst. Electron. Inform. Commun. Eng. D-11, Vol. J71-D-11, no. 7, pp. 1170-1176, 1992)
3) Further, there has published as a thesis in respect to classification of mammary glands: Method for automatically classifying mammograms based on evaluation of density of mammary glands (Japanese Medical Magazine titled “Medical Electronics and Biomedical Engineering” Vol. 38, No. 2, pp. 93-101, 2000)
It has been difficult for a conventional radiation image processing apparatus to output images having a stable gradation characteristic, which, sometimes, varies depending on characteristics of the images, since such the apparatus output each of the images as it is, despite that each of the images was acquired on the different conditions (such as amount of radial rays, voltage applied to radiation tube, screen, film, plate, etc.) or adjust the gradation of each image on the basis of histogram data created from each image. Further, when such the images are used for detecting suspicious regions, sometimes, the variations of the gradation characteristics affect the detecting capability of the apparatus.
In addition, when the images acquired on the different conditions are classified corresponding to the involution degree of mammary glands, sometimes, it has been difficult to obtain accurate and stable classification results, due to the variations of the gradation characteristics.